While standing on a emerald block and have permission level 2:
Hold the item that you want to add a NBT tag to:
Type the following (Without the " " symbols):
"[NBT type];[NBT name];[NBT value]"
NBT types:
n - Number
l - Logic
t - Text
if NBT type is Logic, then NBT value is either 0 (False) or 1 (True).
Example command: "n;Unbreakable;1"
This will Give the NBT tag of Unbreakable to the item in main hand with value 1; This will make the item unbreakable.
The Spooky NBTs! Team
